A photodetector array for acousto-optic signal processors

Abstract

Acousto-optic (AO) signal processors are of interest for processing wide bandwidth signals in real-time. Unfortunately the performance of practical systems is often limited by the photodetector array, which must satisfy conflicting requirements concerning sensitivity, dynamic range, and response/readout time. A recently developed photodetector structure has important potential advantages for this application. It uses the exponential current to voltage relationship obtainable with a profile channel metal oxide semiconductor field-effect transistor to provide a steady state logarithmic relationship between incident light intensity and output voltage and a dynamic range exceeding 70 dB. This paper discusses the design considerations associated with the use of the new photodetector structure in the context of a 128 element photodetector array being developed for realtime processing of wide bandwidth signals. This design uses a series-parallel architecture to provide a minimum exposure time of 1 μs. The photodetector and readout electronics are optimized to provide high sensitivity and response speed for transient signals. Simulation results for the time response to pulse signals and the crosstalk performance are presented. These suggest that the dynamic range exceeds 50 dB for pulses less than 1 μs in duration.